HealthScorer

Macro Calculator

Free macro calculator using Mifflin-St Jeor BMR + ISSN protein guidelines. Cut, maintain, or bulk — we split TDEE into grams of protein, carbs, and.

Last updated: Sources verified:

How the macro split works

The calculator runs three steps in order.

Step 1 — BMR. We use the Mifflin-St Jeor equation, the predictive RMR formula recommended by the Academy of Nutrition and Dietetics since 2005:

Men: BMR = 10·kg + 6.25·cm − 5·age + 5 Women: BMR = 10·kg + 6.25·cm − 5·age − 161

Step 2 — TDEE. BMR is multiplied by an activity factor (1.2 sedentary → 1.9 very active) to estimate total daily energy expenditure.

Step 3 — Goal adjustment + macros.

GoalCalorie shiftProteinFatCarbs
CutTDEE − 5001.6 g/kg27.5% kcalremainder
MaintainTDEE1.8 g/kg27.5% kcalremainder
BulkTDEE + 3002.0 g/kg27.5% kcalremainder

Protein and fat are anchored to evidence-based ranges; carbs absorb whatever calories are left after protein × 4 and fat × 9.

Why the protein anchor matters

The single biggest mistake on a cut is under-eating protein. A 70 kg person on 1.6 g/kg gets 112 g of protein per day; the same person guessing might get 70 g and lose far more lean mass than necessary. On maintenance and bulk, higher protein supports recovery and lean tissue accrual without a meaningful caloric cost (protein is the most satiating macro per kcal).

Adjusting after two weeks

These numbers are starting points. Track the actual scale + tape measurements for 14 days, then:

  • No change in weight when cutting → drop calories by another 100–150 kcal/day or add a daily 30-minute walk.
  • Losing more than 1% body weight per week → add 100 kcal back (you’re risking lean mass loss).
  • No change in weight when bulking → add 150 kcal/day, mostly from carbs.
  • Gaining more than 0.5% body weight per week → drop the surplus by 100 kcal/day (above this rate is mostly fat).

Privacy

All calculation happens in your browser. We never see, log, or store the values you enter. Anonymous, aggregate events (the goal selected) are sent to a privacy-first analytics service.

Frequently asked questions

How much protein do I actually need?
ISSN's 2017 position stand puts the practical range at 1.4–2.0 g per kilogram of body weight per day for active adults. We default to 1.6 g/kg on a cut (preserves lean mass under deficit), 1.8 g/kg on maintenance, and 2.0 g/kg on a bulk (supports recomposition). Sedentary adults can sit at the lower end; serious recomp goals can push to the upper end.
Why does this calculator pick fat at 27.5% of calories?
EFSA's reference range for total fat is 20–35% of energy intake; the IOM cites 20–35% for adults. We anchor at 27.5% because it sits comfortably in the middle, preserves enough fat for hormonal function on a cut, and leaves room for carbs to fuel training. If you train low-carb you can shift fat higher and carbs lower in your tracker.
Are activity multipliers accurate?
Activity factors are estimates and can be off by 200–400 kcal/day for individuals — they assume average movement within each category. After two to three weeks at your calculated TDEE, your scale and measurements will tell you whether to adjust up or down. If you have a fitness tracker, replace the multiplier with measured active calories for a more personalised number.
What's the difference between cutting and bulking calorie targets?
We use −500 kcal/day for a cut (≈1 lb / 0.45 kg per week) and +300 kcal/day for a bulk (slow lean gain). Both numbers are conservative. Aggressive deficits sacrifice lean mass and rebound risk; aggressive surpluses just add fat you'll have to cut later. Slower is almost always sustainable.
Does this work for vegetarians or vegans?
Yes. The macros are macros — the food sources are up to you. Plant-based eaters typically need to be more deliberate about protein quality (combining sources, leucine threshold per meal); the totals don't change, but the distribution across the day matters more.
Does my data leave my device?
No. The calculation runs entirely in your browser. We do not transmit, store, or log your inputs. Anonymous usage events (e.g. which goal was selected) are sent to a privacy-first analytics service to help us improve the tool — no personally identifiable information is collected.

More health calculators

Calculators →

Sources

  1. International Society of Sports Nutrition Position Stand: protein and exercise — Journal of the International Society of Sports Nutrition (ISSN, 2017) (peer reviewed, retrieved 2026-04-27)
  2. A new predictive equation for resting energy expenditure in healthy individuals — American Journal of Clinical Nutrition (Mifflin et al., 1990) (peer reviewed, retrieved 2026-04-27)
  3. Dietary Reference Values for fats — EFSA scientific opinion — European Food Safety Authority (guideline, retrieved 2026-04-27)